Apparatus for suspending particles

ABSTRACT

An analytical device incorporating a system for suspending particles includes a conveying device for positioning a pipetting needle at a distance from the central longitudinal axis of the reaction vessel. Particles are suspended by delivering amounts of liquid reagent to two different positions at a predetermined distance from the central longitudinal axis of a reaction vessel, such delivery generates a flow in the reaction vessel which suspends particles exclusively by injection of liquid, thus avoiding the need for subsequent shaking.

FIELD OF THE INVENTION

The invention relates to an analytical device for suspending particles,and a method of making the suspension. Particularly, the invention issuitable for suspending magnetic microparticles during addition ofreagent in a processing station for automatic DNA detections andimmunoassays.

BACKGROUND OF THE INVENTION

In many methods of analysis, including immunoassays and DNA detections,a solid phase needs to be separated from a liquid phase, andsubsequently washed. The last separation step in the washing process isusually followed by conveyance of the sample to a processing station(for example, an incubator) where reagent solutions are added. In theconventional method of addition, solutions are pipetted into the middleof the reagent vessel through the tip of a pipette. Reagent and solidphase must be well mixed if subsequent chemical reaction is to proceedquickly and efficiently (for example, during incubation). To thoroughlysuspend the solid phase, prior art processes employ a shaking operation.Either the reaction container or the entire processing station areshaken. Such required equipment increases complexity, and thus increasesthe cost and total bulk of the plant. The shaking operation alsodisadvantageously prolongs total processing time.

The subject invention fulfills a long felt need for an apparatus andmethod which suspend particles without requiring an additionalsuspension device or shaking operation.

SUMMARY OF INVENTION

An analytical device is provided for introducing a liquid into areaction vessel to induce mixing within the reaction vessel. The devicecomprises a pipetting device having conveying means for moving apipetting needle in three directions at right angles to one another, anda processing station in which a reaction vessel having a centrallongitudinal axis can be disposed. The processing station is configuredand dimensioned so that a defined amount of a liquid can be pipettedthrough the pipetting needle into the reaction vessel. The processingstation is also configured and dimensioned so that the conveying meansis capable of positioning the pipetting needle at a predetermineddistance from the central longitudinal axis of the reaction vessel, theposition of the pipetting needle relative to the reaction vesselremaining unchanged while the liquid is being pipetted.

Preferably, the pipetting needle is configured and dimensioned to bepositioned in the space between the central longitudinal axis of thereaction vessel and the inner wall of the reaction vessel.

A method of suspending particles in a reaction vessel having a centrallongitudinal axis by introducing a volume of a liquid into the reactionvessel via a pipetting needle movable by a conveying device is alsoprovided. The method comprises the following steps:

First, the conveying device moves the pipetting needle to a firstposition located at a first predetermined distance from the centrallongitudinal axis of the reaction vessel.

Second, the pipetting needle introduces a first predetermined volume ofliquid into the reaction vessel to form a first vortex within thereaction vessel. During this step the position of the pipetting needleremains unchanged while the liquid is being introduced.

Third, the conveying device moves the pipetting needle to a secondposition located at a second predetermined distance from the centrallongitudinal axis of the reaction vessel.

Fourth, the pipetting needle introduces a second predetermined volume ofliquid into the reaction vessel to form a second vortex within thereaction vessel which rotates in the opposite direction to the directionof rotation of the first vortex.

Preferably, the first position is diametrically opposite, relative tothe central longitudinal axis of the reaction vessel, to the secondposition. The diametrically opposite wall regions, relative to thecentral longitudinal axis of the reaction vessel into which the liquidis being delivered, are typically those regions to which particles arealready adhering. Advantageously, the particles can be magneticmicroparticles.

Of great preference is the situation where the first and secondpredetermined distances are equal and adjacent the interior walls of thereaction vessel, and the liquid is ejected from the pipette underpressure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1--A perspective view of an analytical device according to theinvention;

FIGS. 2-5--Illustration depicting the subject process for suspendingparticles;

FIG. 6--A axonometric diagram of the pipette guidance according to theinvention, as per FIGS. 2 to 5; and

FIG. 7--An alternate method of guiding a pipette according to theinvention.

DETAILED DESCRIPTION OF THE INVENTION

The subject invention will now be described in terms of its preferredembodiments. These embodiments are set forth to aid in the understandingof the invention, but are not to be construed as limiting.

An aim of the present invention is to provide an analytical device and ameans for suspending particles, free from the aforementioneddisadvantages. The described problems are solved by an analytical devicehaving the following components: a pipetting device with a conveyingmeans for moving the pipetting needle in three directions at rightangles to one another, at least one reaction vessel having a centrallongitudinal axis, the reaction vessel containing the particles to besuspended, and at least one processing station in which the reactionvessel can be disposed and on to which a defined amount of a reagent canbe pipetted through the pipetting needle into the reaction vessel. Theanalytical device is characterized in that the conveying device is forpositioning the pipetting needle at a distance from the centrallongitudinal axis of the reaction vessel such that the position of thepipetting needle in the reaction vessels remains unchanged whileinjecting the reagent.

The choice of pipetting device, reaction vessel and processing stationis readily determined by a skilled artisan. Moreover, automatedpipetting devices, reaction vessels and processing stations aregenerally well known in the art. To avoid redundancy, an intimatedescription of these components is not provided.

The "distance" is the region between the central longitudinal axis ofthe reaction vessel and the wall thereof.

Processing stations according to the invention can be stations inincubators, washing devices or the like.

Particles according to the invention may be precipitates ofdifficulty-soluble compounds, magnetic microparticles used as carriersin solid-phase DNA detections or immunoassays, magnetic micro-beads, orthe like. Preferably the deposits are magnetic micro-beads.

Pipetting needles according to the invention are preferably designed sothat a reaction container cover can be pierced.

Another aim of the invention is to provide a method whereby particlescan be suspended without the previously described disadvantages, byintroducing a defined amount of a liquid into a reaction vessel.

The present invention provides method of suspending particles in areaction vessel. A predetermined volume of a reagent liquid isintroduced into the reaction vessel by a pipetting needle which ismovable by a conveying device. The conveying device brings the pipettingneedle to a first position at a first distance from the centrallongitudinal axis of the reaction vessel. Once the pipetting needle isat the first position, some of the predetermined volume of reagentliquid is injected into the reaction vessel and forms a first vortex(the position of the pipetting needle in the reaction vessel remainsunchanged while injecting the reagent liquid). The conveying device thenmoves the pipetting needle to a second position at a second distancefrom the central longitudinal axis of the reaction vessel, and when thepipetting needle is at the second position, the remaining part of thepredetermined volume of the reagent liquid is injected into the reactionvessel, forming a second vortex which rotates in the opposite directionto the rotation of the first vortex. Typically, the first and seconddistances are equal in o opposite directions from the centrallongitudinal axis of the reaction vessel. However, the first and seconddistances need not be exactly equal and may be varied to conform withdiffering tube sizes and configurations.

The particles can adhere to diametrically opposite wall regions of thereaction vessel, relative to the central longitudinal axis. This is thecase e.g. when the particles are magnetic microparticles and the solidand liquid phase are first separated by two diametrically oppositemagnets.

The inventive process is suitable for other applications in addition tosuspending particles deposited at diametrically opposite regions on thewall, relative to the central longitudinal axis. After a portion of thepredetermined volume of reagent liquid has been pipetted into thereaction vessel in a first position, the pipetting needle can be rotatedto any desired second position at a distance from the centrallongitudinal axis of the reaction vessel, where the deposited particlesare suspended by adding the remaining part-volume of reagent liquid. Inaddition, a solution already in the reaction vessel can be efficientlymixed with other solutions.

A main advantage of the present invention is that addition of reagentliquid at two different positions in a reaction vessel results in a flowtherein, enabling the solid phase to be suspended exclusively byinjection of reagent, thus avoiding the need for a subsequent shakingoperation. In analytical equipment, the inventive device can produce anoptimum suspension of particles during the addition of reagent, simplyby choosing a suitable program for actuating the pipetting needle, sothat a maximum number of samples can be processed per unit time.

By way of example, the drawings show an analytical device for automaticsolid-phase DNA detections in which the solid phase consists of magneticmicroparticles, and the solid and liquid phases are separated bypermanent magnets. After separation, the microparticles are deposited ontwo diametrically opposite wall regions of the reaction vessel.

FIG. 1 shows an analytical device 1 designed for, among other things,performing DNA detections. The device 1 contains means for performingthe aforementioned DNA detections, in the present case two racks 3, 4with reagents on a vibrating table 5, three racks 7 holding throwaway(disposable) reagent containers 8, a temperature-controlled incubator 9,a washing device 11 and a photometer 12.

Samples, reagents and reagent vessels are conveyed by a conveying device13 movable in an x-y coordinate system. Conveying device 13 comprises apipetting means 14 with a pipetting needle 18 and a reaction vesselgripper 15, both movable in the z direction.

To transfer a reagent, the pipetting needle 18 is moved towards a rack3, 4, where a reagent is withdrawn by suction. The pipetting needle 18is then moved to a reagent vessel 8, where the reagent is delivered.Process parameters can be input via a control panel 16 and/or a bar codewand 17. The CPU controls and coordinates all operations in the process.

FIGS. 2-5 show the method according to the invention for suspendingmagnetic microparticles.

FIG. 2 shows a reaction vessel 8 having a central longitudinal axis 22.The particles 19 adhere to diametrically opposite inner walls of thereaction vessel 8, relative to the central longitudinal axis 22.

FIG. 3 shows the pipetting needle 18 in a first position at a distance efrom the central longitudinal axis 22, where a part of the predeterminedvolume of reagent liquid 21 is injected. The resulting vortex 24 isdiagrammatically shown.

FIG. 4 shows the pipetting needle 18 in the second position at adistance e from the central longitudinal axis 22, where the rest of thepredetermined volume of reagent liquid 21 is injected. The resultingvortex 25 is diagrammatically indicated, showing the reverse directionof rotation.

FIG. 5 is a diagram of resuspended particles. The pipetting needle 18can be adjusted in simple manner by a conveying device 13, using asuitable control program (x-y adjustment).

FIG. 6 shows the linear movement of the pipetting needle 18 at twodiametrically opposite positions relative to the central longitudinalaxis 22. The total travel is 2e.

FIG. 7 shows rotating movement of the pipetting needle 18 at any desiredpositions at a distance e from the central longitudinal axis 22.

The invention has been described in terms of its preferred embodiments.However, upon reading the present specification various alternativeembodiments will become obvious to those skilled in the art. Forexample, travel distance (e) can be readily varied, as can the type ofpipetting device, type of reaction container, processing station, etc.The movement from the first predetermined pipetting position to thesecond predetermined pipetting position could also be effected by movingthe processing station, as opposed to by moving the pipetting needleitself. These variations are to be considered within the scope andspirit of the subject invention which is only to be limited by theclaims which follow and their equivalents.

What is claimed is:
 1. An analytical device for suspending particles ina reaction vessel, which comprises:(a) a processing station into which areaction vessel can be disposed; (b) a pipetting device having conveyingmeans for moving a pipetting needle in three directions at right anglesto one another, and (c) programmable means for controlling the positionof the pipetting needle relative to the processing station so as tocause the pipetting needle to dispense predetermined volumes of liquidat more than one distinct location within the reaction vessel whendisposed at the processing station, the position of the pipetting needlerelative to the reactor vessel remaining unchanged at each locationwhile liquid is being dispensed into the reaction vessel when disposedat the processing station.
 2. The device according to claim 1, whereinthe reaction vessel has an inner wall and a central longitudinal axis,and the programmable means causes the pipetting needle to dispenseliquid into the reaction vessel at a location between the inner wall andthe central longitudinal axis when the reaction vessel is disposed atthe processing station.
 3. The device according to claim 1, wherein thepipetting device dispenses the liquid with a force sufficient togenerate a vortex within the reaction vessel.
 4. The device according toclaim 2 wherein the pipetting needle is configured and dimensioned to bepositioned in the space between the central longitudinal axis of thereaction vessel and the inner wall of the reaction vessel.
 5. Ananalytical device for suspending particles in a reaction vessel havingan inner wall and a central longitudinal axis, which comprises:(a) aprocessing station into which a reaction vessel can be disposed; (b) apipetting device having conveying means for moving a pipetting needle inthree directions at right angles to one another, and (c) programmablemeans for controlling the position of the pipetting needle relative tothe processing station so as to cause the pipetting needle to dispensepredetermined volumes of liquid at a location between the inner wall andthe central longitudinal axis of the reaction vessel when disposed atthe processing station, the position of the pipetting needle relative tothe reactor vessel remaining unchanged at each location while liquid isbeing dispensed into the reaction vessel when disposed at the processingstation.
 6. The device according to claim 5, wherein the programmablemeans causes the pipetting needle to dispense liquid at a plurality oflocations within the reaction vessel when disposed at the processingstation.
 7. The device according to claim 5, wherein the pipettingdevice dispenses the liquid with a force sufficient to generate a vortexwithin the reaction vessel.
 8. The device according to claim 5, whereinthe pipetting needle is configured and dimensioned to be positioned inthe space between the central longitudinal axis of the reaction vesseland the inner wall of the reaction vessel.